In disposing a rigid board over a bending portion of a steel case, generally, the rigid board is divided into a plurality of pieces which are to be connected with one another by utilizing connectors or a flexible board.
In the connecting the rigid board pieces with the connectors or the flexible board, however, the thickness of the thus obtained assembly is increased by the thickness of the connectors or the flexible board so as to prevent the thinning of the intended instrument. Moreover, after the rigid board pieces are connected with the connectors or the flexible board, the same treatment and processing can not be carried out for the rigid board pieces, resulting in the deterioration of productivity.
In this point of view, such a rigid-flexible board as the rigid board pieces with the same thickness is connected to the flexible board so that the main surface levels of the flexible board is equal to or lower than the main surface level of the rigid board pieces.
The rigid-flexible board can be manufactured as disclosed in Japanese Patent Application Laid-open No. 7-86749 wherein a conductive metal plate made of electrolytic copper foil on which conical shaped conductive bumps are formed through hardening so as to protrude thereon and oppose to another conductive metal plate via a thermal melting sheet made of synthetic resin, and then, the conductive metal plates are combined under thermal pressing so as to form a two-sided board. However, such a manufacturing method requires many steps as follows (see, Patent document No. 1). Herein, the same reference numerals are imparted to like components throughout figures, so that the description for like components is omitted.
Such a conventional technique will be described hereinafter with reference to FIGS. 17-23. In the conventional technique, first of all, as illustrated in FIG. 17, a two-sided flexible board 2 is formed so that the edge portions are not covered with a cover film 1. The not covered area of the flexible board 2 with the cover film 1 is laminated on a rigid board. In FIG. 17, the reference numeral “3” designates a liquid crystal polymer film, and the reference numeral “4” designates a horizontal wiring area (conductive pattern), and reference numeral “5” designates a vertical wiring area (conductive bump).
The vertical wiring area 5 can be formed using the conductive bump as follows. First of all, the conical conductive bump is formed on an electrolytic copper foil to be the horizontal wiring area 5 through patterning as post-process, and the conductive bump is opposed to another electrolytic copper foil via the liquid polymer film (synthetic resin sheet) 3. The electrolytic copper foils are combined through thermal pressing. In this case, the forefront of the bump is pressed against the electrolytic copper foil so as to be plastic-deformed into a circular cone shape as functioning as the vertical wiring area 5 to connect the horizontal wiring areas 4. The horizontal wiring areas 4 can be formed by applying resist on the electrolytic copper foils, exposing the resist through a mask pattern, removing the unexposed area through developing and etching the exposed area of the electrolytic copper foils.
The cover film 1 can be formed by applying resist on the electrolytic copper foils after etching and removing the area to be combined with the rigid board through photolithography.
As illustrated in FIG. 18, the flexible board 2 is combined with a laminated body 6 (the reference numeral “7” designates a releasing film) with a conductive bump 5a which is made in another forming process so as to be a laminated body 9 as illustrated in FIG. 19.
The laminated body 6 can be formed as follows. A conical conductive bump is formed in an electrolytic copper foil to be the horizontal wiring area 4 after etching as post-process, and the electrolytic copper film is combined with another electrolytic copper film 4a via a glass-epoxy based prepreg (synthetic resin based sheet) 3a so that the conical conductive bump is opposed to the electrolytic copper foil 4a. In this case, the forefront of the conductive bump is pressed against the electrolytic copper foil 4a so that the forefront of the conductive bump is plastic-deformed into a circular cone shape as functioning as the vertical wiring area 5 to connect the electrolytic copper foils 4a. Then, one of the electrolytic copper foil is patterned into the horizontal wiring area 4. Then, a conductive bump 5a is formed at the position of the horizontal wiring area 4 corresponding to the vertical wiring area 5, and a synthetic resin sheet 3a is formed so that the forefront of the conductive bump 5a protrudes through and is combined with the sheet 3a. 
The combination between the laminated body 6 and the flexible board 2 is performed by aligning the side wherein the conductive bump 5a protrudes for the exposed surface area (not covered area with the cover film 1) of the horizontal wiring area 4 of the flexible board 2, and performing thermal pressing (FIG. 19). In this case, a slit 8 is formed at the interface between the laminated body 6 and the flexible board 2, and a releasing film 7 as functioning as a spacer is formed on the surface of the flexible board 2 opposing to the cover film 1.
As illustrated in FIG. 20, the laminated body 9 is combined with a laminated body 10 made in another processing through thermal pressing so that the flexible board 2 is contacted with the laminated body 10. In this way, a laminated body 11 is formed (FIG. 21).
The combination between the laminated body 9 and the laminated body 10 is performed as follows. First of all, the conductive bump 5a protruding from on the laminated body 10 is contacted with the horizontal wiring area 4 of the laminated body 9 (flexible board 2). Then, the releasing film 7 as functioning as a spacer is formed on the surface of the laminated body (flexible board) 2 opposing to the cover film 1. Then, the laminated body 10 is laminated on the laminated body 9 so as to form a laminated body 11 with eight horizontal wiring areas 4 through thermal pressing as illustrated in FIG. 21.
Then, as illustrated in FIG. 22, the outer horizontal wiring (outer pattern) 4 is patterned, and insulating protective films 12 are formed of resist, and as illustrated in FIG. 23, the portions A and B covering the flexible board 2 are removed so as to form the intended rigid-flexible board.
Patent Document No. 1: Japanese Patent Application Laid-open No. 7-86749